Clock signal extraction apparatus

摘要

A plurality of clock signals at an identical frequency but with different phases are oscillated by a voltage-controlled oscillator beforehand, and selection is made of one of the clock signals whose phase is closest to that of the data signal each time the data signal rises. In parallel with the selection of phase and frequency, comparison is made between any one of the clock signals output from a voltage-controlled oscillator and the selected clock signal, and the oscillation frequency of the selected clock signals. After the comparison, the oscillation frequency of the voltage-controlled oscillator is converted for their matching. This matching allows acquisition of a clock signal with the closest phase immediately after arrival of the data signal, and acquisition of an extraction clock signal with the frequency and phase are matched in a short time by parallel conversion of the oscillation frequency of the voltage-controlled oscillator. <IMAGE>